Conventionally, there is known an internal combustion engine that promotes combustion of fuel injected from an injector to a combustion chamber by way of electromagnetic wave plasma (such as microwave plasma). For example, Japanese Unexamined Patent Application, Publication No. 2009-207549 discloses an internal combustion engine of this kind.
More particularly, in the internal combustion engine disclosed by Japanese Unexamined Patent Application, Publication No. 2009-287549, while a piston is in the vicinity of a top dead center, an injector injects fuel. Then, the injected fuel is ignited, and a flame is formed. A microwave pulse is supplied to a region in the vicinity of the flame, and electrons in the flame are energized and accelerated. The accelerated electrons collide with ambient molecules. The collision molecules are ionized to form plasma. Electrons in the plasma are also energized and accelerated, and ambient molecules collide with the electrons to form plasma. Thus, in the internal combustion engine, an avalanche-like plasma generation occurs. As a result of this, comparatively large microwave plasma is generated.